fixing name of PuBuGn colormap in default_colormaps.py
fixing name of PuBuGn colormap in default_colormaps.py

tommy-u/chaco,tommy-u/chaco,ContinuumIO/chaco,ContinuumIO/chaco,burnpanck/chaco,burnpanck/chaco,tommy-u/chaco,burnpanck/chaco,ContinuumIO/chaco,ContinuumIO/chaco